Our overall objective is to enhance understanding of vestibular function by aiding in the identification of substances involved in neural transmission in various physiologically and/or morphologically characterized vestibular pathways. For this purpose, we will initiate systematic studies on the distribution of the putative amino acid transmitters, GABA, glycine, aspartate, and glutamate in the vestibular nuclear complex of the cat. These studies are intended to establish comprehensive three-dimensional quantitative histochemical maps of the vestibular system similar to those recently provided for the cochlear nuclei. Our first aim is to correlate the generated quantitative histochemical patterns to the somatotopic organization of the vestibular nuclei. In order to provide a precise three-dimensional framework for the mapping of forthcoming histochemical patterns and for correlation of physiological data, we propose to generate a "block model" of the vestibular nuclear complex analogous to that already available for the cochlear nuclei. Next, we intend to study the short term effects of interrupting selected physiologically and/or morphologically characterized afferent vestibular pathways upon the levels of these amino acids. For this purpose we will ablate a) the cerebellar flocculus; b) the nodulus-uvula; and c) the vestibular endorgans; we will section the vestibular nerve; and we will lesion the commissural vestibular pathways. In addition, we will study the biochemical counterparts of vestibular compensation following labyrinthectomy and vestibular neurotomy. Furthermore we intend to investigate potential biochemical correlates of vestibular sensory deprivation in young kittens. We will also characterize the efferent vestibular system to the periphery with respect to enzymes of the cholinergic system by a combination of qualitative and quantitative histochemical methods.